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The worldwide development of mobility - on air, earth or water - is generally characterized by a trade-off between high power and high torque against low specific energy consumption and low pollutant emission. The achieved diversity of propulsion systems and energy sources for mobility allows to develop advantageous combination scenarios between the utilized energy forms, energy conversion modules, energy storage units on board and propulsion machines. The paper presents the available energy sources and the derivable regenerative fuels, the global CO2 balance for representative propulsion configurations and the specific aspects of the energy storage on board. The most advanced concepts of propulsion - from fuel cells to the hybrid systems are presented in an overview, in relationship with their specific advantages and disadvantages.

Going from the example of the urban traffic in Europe, where the car use in town areas generally do not exceed 50 km/day, a series hybrid vehicle with light and compact thermal engine as an auxiliary power unit (APU) is demonstrated to be a promising concept. The paper describes such a configuration in base of a developed two-stroke engine with electronically controlled gasoline direct injection. The injection system is characterized by a high-pressure modulation obtained in base of the water hammer effect, which can be accurately adapted for a wide load and speed range of the engine. In this assembly the engine has extremely small dimensions and a dry weight of 8 kg, requiring a place which do not disturb the functions of the basic electric vehicle. The performances are convicting, the CO2 emission being reduced 3 times in comparison with a series four-stroke engine for the same car type, with an autonomy of 340 km and with a maximum speed of 100 km/h.

The propulsion of future motorcycles and small vehicles will be determined by the reduction of dimensions, weight, fuel consumption and pollutant emission for a considered power output, implicating an improved control of the internal process stages consisting on scavenging, mixture formation and combustion. A main support of such process improvement is the internal mixture formation by gasoline direct injection. However, the compactness and the high-speed range of a small engine for two-wheelers, marine or garden equipment make the application of direct injection more difficult than for automotive engines. On the other hand, after the initially tested wall- and air- guided techniques, it is generally recognized that the only way for a successful large scale utilization of gasoline direct injection is the spray-guided mixture formation.